SCHiNCH-GOSS//\ 



^17 



cimstitution as will cause pereolutinn walcr to ilc-posit 

 any miiliTial lluit It liolds in solulii)n. I may Siifcly 

 state tlut in no rase where it is in the renmtest con- 

 linnency piissible to refer the manganese ti> " I'rimary 

 l''iltrati()n," do we lind this essential rondition present. 

 Indeed, the only cases in which we find an impervious 

 lied beneath the seams, are those in whicli such seams 

 (icciir at the base of the gravel and the underlying 

 depasit is clay. .Such seams are of considerable 

 thicknesi as a rule, and' moreover extend over a 

 ironsiderable area. Kor instance, I recently traced 

 one at the base of the High Terrace gravel of 

 Acton for a distance of 250 yards. Such examples as 

 this, clearly owe their position 10 '" Secondary 

 Filtration." 



[2.) Contcniporancou> I'luvialilc Ik-pusiiion. Let 

 us suppose that we have a river llowing through an 

 area in which ores of manganese, preferably di-oxide, 

 occur in some abundance. During the denudation of 

 such an area, the manganese, as successive deposits of 

 ii are attacUeil, will be carried down in suspension 

 or chemical solution by the river. .-\s the manganese 

 from the various deposits will have approximately the 

 same specific gravity, it will have a tendency to 

 collect in certain places. If the water becomes super- 

 charged with the soluble mineral, or if chemical 

 change takes place cither through some alteration in 

 the- constitution of the bed of the river, or through 

 some influx of other matter; then the manganese will 

 be precipitated and will encrust the sedimenlaiy 

 material forming on the bottom. There are three 

 reasons why precipitated manganese will not penetrate 

 the sediment to any great extent. In the first place 

 if the bottom is argillaceous, then such non-penetra- 

 tion must obviously occur. When, however, the bed 

 of the river is gravel or of similar porous material, 

 some other reasons have to be found for the non- 

 penetration. The chief, in such cases is that 

 encrustation goes on almost simultaneously with 

 precipitation ; and secondly, the mineral now 

 rendered insoluble meets with the resistance of the 

 water that saturates the gravel which forms the 

 hoUoin. 



.Vdopting this theory we find thai the field- 

 evidence supports it in every respect. !■!}■ it we can 

 explain the occurrence of continuous seams in stiff 

 impervious loams and clays, in gravels in which no 

 impervious material underlies the manganese, and in 

 which the seams of gravel so staine<l are not different 

 Irom the other beds in their constitution or porosity, 

 or if they are more impervious, essentially owe this 

 character to the presence of the manganese. 

 Furthermore, we can explain by it how the overlying 

 and underlying beds are entirely unaffected b\- these 

 seams, which would not be the case in the majority 

 ol instances, if filtration produced them. 



There is one more point to which it is necessary to 

 refer. Where is the source from which ilu- manganese 

 was derived ? We. have in the Thames \ alley no 

 manganese bearing strata other than the drift, or, at 

 le.ast, no deposit capable of supplying the t|uantity 

 lounil in the drift. In the discussion following my 



I'' 



paper, Ijefore alluded to, Mr. A. V.. Sailer, l''.(i..S., 

 siud that it was just |)ossible that Wales was the 

 parent source. The recent [ihysiographical researches 

 of I'rof. U.avis and .Messrs. Kucknian and White, have 

 tended to show that the Thames once lloweil from 

 Wales across what is now the .Severn valley. If this 

 be the case, then we have a source for our manganese, 

 and at present I can only adopt .Mr. Salter's view. 

 M all events, in the light of our present knowledge, 

 it is impossible to otTer a belter one. In conclusion, 

 our dilViculties in this respect are enhanced because of 

 the fact that we cannot base too much reliance, if any 

 at all, on the manganese being in the position in which 

 it was first deposited, after its derivation from the 

 parent strata. 



cjoj. C. Graham, 2, Garden Court. 

 Temple, London, F..C. 



CROMWELL RO.UJ AIL.M-.L.M. 



' P 1 1 1 . collections in the Natural History Museum 

 ■^ at South Kensington have lately been enriched 

 by specimens obtained by various exploring expe- 

 ditions. The zoological branch benefited greatly by 

 the expedition to .Sokotra, which was organised by 

 Mr. W. R. Ogilvie-Grant, representing the lirili.sh 

 Museum, and Dr. II. O. Forbes, director of the 

 Liverpool Museum, under the auspices of the Koyal 

 Geographical Societies and the British .Vssociation. 

 The lepidoptera obtained are specially numerous 

 some of the species being hitherto unrecorded. 

 Eight new species of reptiles, twenty species of 

 marine fish, large collection of shells and insects, and 

 many other fliuna were obtained. 



Another expedition that has yielded results of 

 considerable interest to the geological and zoological 

 sections is the one from which Dr. J. \V. Gregory, of 

 the geological Department, has just returned. His 

 object was to examine the geology of .\ntigua. 



Some acquisitions of particular interest were 

 obtained by means of the exoedition sent out by the 

 Hon. Walter Rothschild to the fialapagos .Archipelago 

 ofl" the Coast ol Ecuador. Amongst others was a 

 fine example of the rapidly diminishing gigantic land 

 tortoises, also a series of five hundred birds, and a 

 large collection of reptiles. 



Mr. Welt Blundell and Lord Lovat ha\e presented 

 to the trustees the fine series of birds made by them 

 during their recent adventurous journey in .\byssinia. 

 The collection, consisting of 530 specimens of 234 

 species, has not yet been thoroughly examined, but 

 the ornithologists of the Museum are convinced it is 

 of the greatest interest. 



Since the departure of the mission dispatched to 

 Sierra Leone by the Liverpool School of Tropical 

 Di-seases, for the investigation of malaria, hundreds of 

 mosquitoes have been sent to the British Museum 

 from every pan of the British Empire, and it seems 

 probable the museum will soon be in possession of an 

 unique collection of the genus Cn/e.v. Mr. E. .\usten, 

 the dipterologist of the Museum, is a member of 

 Major Ros,s" party, and will endeavour as fir as 

 possible to make collections of other groups. 



